JPH07102525A - Wind-resistant vibration mitigating structure in building suspension bridge - Google Patents

Abstract

PURPOSE:To provide a wind-resistant vibration-mitigating structure for use in building a suspension bridge, wherein the construction thereof is simple and is of low cost and economical. CONSTITUTION:In a suspension bridge wherein there are provided a pair of forward and rearward portal-frame towers 1, 1 which are opposedly spaced a proper interval in the forward and rearward direction, and a left side main cable 2 and a right side main cable 2 are stretched between the upper ends of the towers, when the building of the main cables is completed, an inclined connecting wire 3 is provided to connect a point spaced along the main cable a little from a fixing point of the cable 2 at the upper end of one of the tower 1 with a point a little below the upper end of the tower 1. And the wires 3 are provided for the left side main cable and right side main cable respectively. Further, the wires 3 are not parallelly provided, but provided crosswise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wind-resistant and vibration-proof structure for constructing a suspension bridge.

[0002]

2. Description of the Related Art It has been estimated that, in a suspension bridge, a main girder vibration phenomenon due to strong winds occurs even at a relatively low wind speed during erection than after completion. However, since there is no effective vibration control means for this structure, aerodynamic measures such as simply changing the shape have been mainly adopted.

[0003]

That is, in a long suspension bridge, it is unavoidable that the vibration phenomenon of the main girder called flutter due to strong winds becomes a design problem, and sometimes the structure becomes softer after completion. Whether or not the wind speed at which flutter occurs exceeds the allowable wind speed during erection may determine the wind resistance. On the other hand, as a method of erection of girders of suspension bridges, a method of starting erection from the central part of the center span and extending the girder in the front-rear direction toward the tower is often advantageous in terms of wind resistance It is considered that this method cannot be adopted because it is inferior. As a vibration control measure that raises the fluttering wind speed during installation, it is difficult to make it rigid due to its structure.Therefore, large-scale aerodynamic measures such as changing the shape of the main girder must be used. The reality is that it is not possible to implement it easily.

The present invention has been proposed in view of the above circumstances, and an object thereof is to provide a wind resistant vibration-damping structure for constructing a suspension bridge which is simple in structure, low in cost, and economical.

[0005]

To this end, the invention according to claim 1 is between the upper ends on the same side of a pair of front and rear gate-shaped towers which are erected so as to face each other with a proper distance in the front-rear direction. In a suspension bridge in which a left main cable and a right main cable are stretched, when the above main cables have been erected, from the same fixing point of the main cables fixed to the upper end of one tower, along the same main cables It is characterized in that an oblique connecting wire is provided to connect a part which is slightly separated to a part which is slightly below the upper end of the tower.

According to a second aspect of the present invention, in the first aspect, the diagonal connecting wires are provided on the left main cable and the right main cable, respectively.

According to a third aspect of the present invention, in the first aspect, the slightly lower part of the left upper end of one of the towers is diagonally stretched with respect to the right main cable instead of being diagonally stretched with respect to the left main cable. In addition, instead of diagonally stretching the lower part of the upper right end of the same tower diagonally to the right main cable, diagonally stretch it to the left main cable so that both diagonal connection cables are hooked. It is characterized by being provided.

[0008]

According to this structure, the middle portion of the main cable and the middle tower are connected by the diagonal connecting wires when the suspension bridge is installed, and the restraining force acts on the vertical displacement of the main cable. Then, in the vibration mode of the main girder vertical bending mode, the vertical bending displacement of the main cable is as excellent as that of the main girder, so that the vibration mode of the main girder also changes. By applying this measure to only one of the two towers, the symmetry of the vibration mode shape is broken. Here, since the main girder twist mode is less affected, the similarity between the two modes is reduced and the flutter generation wind speed is increased. Further, as the effect of the vibration suppression measure according to the present invention, in addition to the reduction of the mode similarity, an increase in the frequency and an increase in the equivalent weight (polar moment of inertia) can be expected as additional effects, and these also increase the fluttering wind speed. Perform the action of causing.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall side view showing the first embodiment, FIG. 2 is a perspective view showing the tower portion of FIG. 1, and FIG. FIG. 4 is a diagram showing the flutter of the cable, FIG. 4 is a perspective view showing the main tower portion of the second embodiment, and FIG. 5 is a perspective view showing the main tower portion of the third embodiment.

First, the first embodiment will be explained. As shown in FIG. 1, the construction of the tower 1 and the main cable 2 is completed,
The main girders are in a state of being extended on both sides from the central part of the main girder 3 toward the tower. Here, as shown in FIG. 2, the damping wire 4 as a damping measure is installed only in the tower on the right side of the figure,
The tower and the main cable are connected in a nearly triangular structure.

Then, the vertical bending vibration mode shape 5
As shown in FIG. 3, the left-right symmetry is broken as compared with the shape 6 shown in FIG. 6 in the case without the conventional vibration suppression measures, and an effect of increasing the flutter generation wind speed is obtained. The damping wire of the first embodiment is one in which diagonal damping wires are installed for each of the two main cables of the suspension bridge. As another installation method, as shown in the second embodiment (FIG. 4), one of the two surfaces of the main cable is used.
A method of installing only on the surface, or a method of installing in an X shape as shown in the third embodiment (FIG. 5) can be considered. According to this structure, the middle part of the main cable and the middle part of the tower are structurally connected by the damping wire when the suspension bridge is installed, and the restraining force acts on the vertical displacement of the main cable. Then, in the vibration mode of the main girder vertical bending mode,
Since the vertical bending displacement of the main cable is as excellent as that of the main girder, this also changes the vibration mode of the main girder. By applying this measure to only one of the two towers, the symmetry of the vibration mode shape is broken. Here, the influence of the main girder twist mode is small, so the similarity between both modes is reduced,
The fluttering wind speed increases. Further, as the effect of the vibration suppression measure according to the present invention, in addition to the reduction of the mode similarity, an increase in the frequency and an increase in the equivalent weight (polar moment of inertia) can be expected as additional effects, and these also increase the fluttering wind speed. Perform the action of causing.

[0012]

By implementing the present invention, there is no restriction on the wind resistance of the construction method of the suspension bridge, and the suspension bridge can be easily constructed.

In short, according to the inventions of claims 1, 2 and 3, it is possible to provide a wind resistant vibration damping structure for constructing a suspension bridge which is simple in structure, low in cost and economical, and therefore the present invention is industrially applicable. It is extremely useful.

[Brief description of drawings]

FIG. 1 is an overall side view showing a first embodiment of the present invention.

FIG. 2 is a perspective view showing a tower portion of FIG.

FIG. 3 is an overall side view showing a flutter mode of the main cable in FIG.

FIG. 4 is a perspective view showing a tower portion of a second embodiment of the present invention.

FIG. 5 is a perspective view showing a tower portion of a third embodiment of the present invention.

FIG. 6 is an overall side view showing a suspension bridge without conventional vibration damping measures.

[Explanation of symbols]

 1 tower 2 main cable 3 main girder 4 damping wire 5 main girder vertical bending mode (present invention) 6 main girder vertical bending mode (conventional suspension bridge)

Claims (3)

[Claims] 1. A left-side main cable and a right-side main cable are stretched between upper ends of a pair of front and rear gate-shaped towers which are erected so as to be opposed to each other with a proper distance in the front-rear direction. In the suspension bridge, when the installation of the main cable is completed, the part slightly apart along the main cable from the same fixing point of the main cable fixed to the upper end of one tower is located slightly below the upper end of the tower. A wind-resistant vibration-damping structure at the time of erection of a suspension bridge, which is provided with a diagonal connecting wire connected to the 2. The wind-vibration damping structure at the time of constructing a suspension bridge according to claim 1, wherein the diagonal connecting wires are provided on the left main cable and the right main cable, respectively. 3. The tower according to claim 1, wherein a slightly lower portion of the upper left end of one tower is stretched obliquely with respect to the right main cable instead of being diagonally stretched with respect to the left main cable. It is characterized in that both diagonally connected cables are provided in a hooked shape by diagonally stretching the left main cable instead of diagonally stretching the slightly lower part of the right upper end of the right main cable. A wind-resistant vibration control structure when constructing a suspension bridge.